Aluminum alloys



Patented @et. l, 1%33 ALUBEW ALLQYS Walter A. Dean and Louis W. Kempi,Ulevcland, (this, assignors to Aluminum Company of America, littsburgli,?ennsylvania Pa, a corporation of No Drawing. Application September 21,1932 Serial No. 034,159 7 This invention relates to aluminum base alloyswhich have excellent properties at elevated temperatures, which aregenerally adapted to foundry purposes and which are insensitive to thecommon impurities found in commercial aluminum.

A good foundry alloy which will retain a substantial proportion of itsphysical and tensile properties at elevated temperatures is constantlybeing searched for in the field of light metals. By light metals is notmeant the ordinary aluminum base. alloys but only such of those alloysas contain substantial amounts of a metal lighter than aluminum so as tocompensate in the alloy for the addition of metals heavier thanaluminum. To provide such an alloy of good foundry characteristics andexcellent strength at high temperatures is the object of this invention.

The aluminum base alloys containing magnesium are lighter than aluminum.They should therefore be excellent material from which to manufacturereciprocating parts which operate at elevated temperatures were it notfor the fact that these alloys at elevated temperatures (such as 400 to700 Fahrenheit) do not have the strength, the ductility and the hardnesswhich are so often necessary. Moreover, the binary aluminum-magnesiumalloys are somewhat lacking in the required foundry characteristics.

We have discovered, after extensive experimem tation, an aluminum basealloy containing magnesium which fulfills, to a surprising extent, therequirements above mentioned. This alloy is one containing 3.0 to 8.0per cent by weight of magnesium, 0.5 to 4.0 per cent by weight ofmanganese, and 0.5 to 4.0 per cent by weight of nickel, the balancebeing principally aluminum. This alloy, we have discovered, hasexcellent foundry characteristics, being capable of use either in sandor permanent molds. The alloy is light, is strong and hard and possessesthese latter properties to a substantial extent at high temperatures.The alloy is, moreover, constant in its properties over long periods athigh temperature and is therefore a very dependable engineeringmaterial. Also the alloy is insensitive to impurities, which is to saythat its properties are not materially afiected by the varying amount ofimpurities, such as iron, which may be found in the commercial aluminumfrom which it is usually made.

The tensile strength of the alloy is high at elevated temperature andits elongation, a measure of ductility, is adequate. It retains thishigh strength at elevated temperatures over long periods withoutsubstantial change and does not become brittle. Examples of the strengthand ductility of the alloys will be found in Table I where are listedthe tensile strength and elongation of. three sand castings made of thealloy, anhealed for 4 hours at 700 Fahrenheit, 20 days at 600Fahrenheit, and finally tested at the lat- Q30 to! temperature.

For comparison it may be stated that a binary aluminum-magnesium alloycontaining 6 per cent magnesium and in sand cast form had, after asimilar thermal treatment, a tensile strength of only 15,000 pounds persquare inch and an elongation of 5 per cent in 2 inches.

The constancy of the properties of our new alloys is well illustrated bya comparison of one of the alloys in sand cast form with a sand cast ingmade of a well known aluminum alloy containing copper. Sand castingsmade of an alloy containing S per cent magnesium, 1.0 per cent 35manganese, and 1.5 per cent nickel, balance aluminum, were annealed for2 hours at 550 Fahrenheit, the temperature was then increased to 600Fahrenheit and the alloys tested at that temperature and'then againtested at the expiration of 99 20 days at 600 Fahrenheit. Similartreatment was afforded sand castings made of an alloy containing 10 percent copper, 0.2 per cent magnesium, 1.2 per cent iron, balancealuminum, and these castings were similarly tested The results 5 areshown in Table II.

A comparison of the values given in Table 11 will demonstrate that thealuminum-copper al- 10y lost about 42 per cent of its tensile strengthin 20 days at 600 Fahrenheit while the tensile strength of thealuminum-magnesium-manganese-nickel alloy remained practically constant,losing only about 7 per cent.

The aluminum-magnesium-manganese-nickel alloys to which this inventionrefers have certain preferred forms. Within the composition limits abovedescribed, the alloys are satisfactory for most purposes, but we havefound the best combination of properties in alloys containing 3.5 to 6.5per cent by weight of magnesium, 0.5 to 2.0 per cent by weight ofmanganese, and 0.5 to 3.0 per cent by weight of nickel, balanceprincipally aluminum. Excellent casting characteristics are found in analloy containing 6 per cent by weight of magnesium, 1 per cent by weightof manganese, and 1.5 per cent by weight of nickel, balance principallyaluminum. We have likewise discovered that certain other elements may beadded to the alloy to effect particular purposes without materiallyharming the leading properties of the alloy. For instance:

If a higher tensile strength or hardness is required in thealuminum-magnesium-manganese nickel alloys which form the subject ofthis invention, the addition of cobalt or chromium may be resorted to inmany cases. We have found that these elements, in certain amounts, willproduce the desired result without seriously depreciating the ductilityof the alloy. If chromium is added it should be in amounts of 0.1 to 2.0per cent by weight, amounts of 0.1 to 0.5 per cent being preferred. Ifcobalt is added it should be in amounts of 0.1 to 2.0 per cent byweight, amounts of 0.1 to 0.5 per cent being preferred.

The alloys which are herein described may be made by any of the usualmethods of compounding alloys, care being taken, of course, not tooverheat or dross the metal during alloying.

Another property of these alloys is their improved fiuidity as comparedwith the alloys which have, heretofore, been widely used as a materialfor parts operating at elevated temperatures. Comparative tests, basedupon the distance that the molten alloy, originally heated to a giventemperature, will flow through a spiral formed in a sand mold, haveshown that out novel alloys are very superior with respect to fluidity.

The aluminum used in the manufacture of the alloys may be of the highestpurity or it may contain amounts of usual impurities, and the termaluminum as used herein and in the claims designates the aluminum ofcommerce. It is an incidental property of our alloys that the presenceof iron in amounts as high as 2 per cent by weight is not harmful to thehigh temperature properties of the alloys and, therefore, a wide choicebetween the various grades of commercial aluminum is possible.

We claim:

1. A metallic alloy characterized by high physical and tensileproperties at elevated temperatures and good fluidity and consisting of3.0 to 8.0 per cent by weight of magnesium, 0.5 to 4.0 per cent byweight of manganese, 0.5 to 4.0 per cent by weight of nickel, and 0.1 to2.0 per cent by weight of cobalt, the balance being aluminum.

2. A metallic alloy characterized by high physical and tensileproperties at elevated temperatures and good fluidity and consisting of3.0 to 8.0 per cent by weight of magnesium, 0.5 to 4.0 per cent byweight of manganese, 0.5 to 4.0 per cent by weight of nickel, and 0.1 to0.5 per cent by weight of cobalt, the balance being aluminum.

WALTER A. DEAN. LOUIS W. KEMPF.

